The present invention relates generally to an electronic over-acceleration and over-speed protection system for an elevator.
Elevators include a safety system to stop an elevator from traveling at excessive speeds in response to an elevator component breaking or otherwise becoming inoperative. Traditionally, elevator safety systems include a mechanical speed sensing device typically referred to as a governor and safeties or clamping mechanisms that are mounted to the elevator car frame for selectively gripping elevator guide rails. If the hoist ropes break or other elevator operational components fail, causing the elevator car to travel at an excessive speed, the governor triggers the safeties to slow or stop the car.
The safeties include brake pads that are mounted for movement with the governor rope and brake housings that are mounted for movement with the elevator car. The brake housings are wedge shaped, such that as the brake pads are moved in a direction opposite from the brake housings, the brake pads are forced into frictional contact with the guide rails. Eventually the brake pads become wedged between the guide rails and the brake housing such that there is no relative movement between the elevator car and the guide rails. To reset the safety system, the brake housing (i.e., the elevator car) must be moved upward while the governor rope is simultaneously released.
One disadvantage with this traditional safety system is that the installation of the governor, including governor and tensioning sheaves and governor rope, is very time consuming. Another disadvantage is the significant number of components that are required to effectively operate the system. The governor sheave assembly, governor rope, and tension sheave assembly are costly and take up a significant amount of space within the hoistway, pit, and machine room. Also, the operation of the governor rope and sheave assemblies generates a significant amount of noise, which is undesirable. Further, the high number of components and moving parts increases maintenance costs. Finally, in addition to being inconvenient, manually resetting the governor and safeties can be time consuming and costly. These disadvantages have an even greater impact in modern high-speed elevators.